This invention relates to machines for cutting sheet material, and deals more particularly with improvements in the construction of the knife and knife holder assembly of such a machine.
The knife and knife holder assembly of this invention may be used with various different types of sheet material cutting machines, but it has particularly utility as part of a machine, such as shown by U.S. Pat. No. 4,467,525, for cutting signs or other graphics from laminated sheet material. In an exemplary case, the laminated sheet material used for sign-making purposes consists of a carrier layer of paper or the like having one face coated with a silicone or other release agent. A layer of colored vinyl or the like is superimposed on this release face of the carrier sheet and held to it by a thin layer of pressure sensitive adhesive which stays with the vinyl when the carrier sheet and vinyl are separated, and which is subsequently used to attach the characters or other graphics cut from the vinyl to a supporting surface.
In the cutting of characters and other graphics from the vinyl of the laminated sheet material the cutting knife should penetrate entirely through the layer of vinyl and the layer of adhesive, so as to completely separate the graphics from the remainder of its vinyl, but the knife should only slightly, if at all, penetrate the carrier sheet, so that the carrier sheet remains intact during and after the cutting process.
It is therefore essential that the depth of penetration of the cutting knife be accurately controlled to a tolerance of plus or minus about one thousandth of an inch or less. The knife and its holder may be spring and/or gravity biased toward the sheet material being cut; and a shoe surface engagable with the top surface of the sheet material may be provided on the holder to limit the downward movement of the holder and knife, but this is not sufficient to insure, with a standard mounting of the knife to the holder, the proper degree of knife penetration. First of all, the thickness of the vinyl and adhesive layers, and possibly other layers, to be cut through by the knife before reaching the carrier layer may vary from one piece of laminated sheet material to another. Further, it is often desired that the knife be of a simple disposable type allowing it to be discarded when dull and replaced by a fresh knife. The manufacturing tolerances on such disposable knives may be such as to allow for a slight variance in knife length from one knife to another so that when a dull knife is replaced by a new one the new one may not have the same degree of penetration as the old.
The general object of this invention is therefore to provide a knife and knife holder avoiding the above mentioned problems, the construction more particularly being such that the knife can be readily removed from and replaced into the holder and the holder including a member providing a shoe surface which member is easily vertically adjustable to adjust the degree of penetration of the knife into the sheet material being cut.
Other objects and advantages of the invention will be apparent from the following detailed description of a preferred embodiment of the invention and from the accompanying drawings and claims.